Rusty Messages: 984 Registered: May 2018 Location: Kansas City Missouri
Illuminati (2nd Degree)
I assembled my preamp kit back a few now that I really enjoy. It has an internal phono circuit which is very nice too. But I'd like to put an output jack on the back panel to send all input signals to so that I can utilize the Aphex Aural Exciter I've use for years with my old phono preamp, a Graham Slee unit. It may be sacrilege for purists but I like it's effect bringing presence and definition with recorded music. They're used in recording studios quite a bit. As is now the inputs go to the selector switch, then on to the volume pot. I though of using a two way on-on to facilitate this idea. Here's a crude rendering of what I'm-a-thinkin.
I just wanted to know it this is feasible like shown. I wanted to be able to keep the signal routing somewhat like it is now and being able to use the Aphex with all inputs too. I don't know if switching while active would cause some nasty pop's or not. But if so, I could just refrain from that. But, maybe there's a better implementation for this scheme of mine. Which I present to people here in the know. Appreciate the input for the output.
gofar99 Messages: 1843 Registered: May 2010 Location: Southern Arizona
Illuminati (5th Degree)
Hi Rusty, It will likely work OK. My major concern is if there is a serious impedance mismatch that could mess up the sound. It could be too high feeding into a low Z input or the other way around. The first would likely cause serious loss of high freqs, the other loss of bass. There could also be an issue with differing signal strength. One very loud the other not so. Yes a pop could occur if any of the outputs has a coupling capacitor that gets slightly charged up above zero on the output side. Most designs use a sort of bleeder resistor (1meg seems common) to eliminate this problem. Anyhow worth a try. Let us know how it goes.
Rusty Messages: 984 Registered: May 2018 Location: Kansas City Missouri
Illuminati (2nd Degree)
I'm trying to understand some of the terminology Bruce. My knowledge of electronics is rather thin. The Aphex unit has a switch to accommodate consumer level gear if that's part of what your conveying. My original thought was kind of like how I'd used it prior which was from a stand alone phono into the Aphex then into any input of the preamp. Just that this preamp now has the internal RIAA circuit built in, so I'd wondered if an added output would function about the same as how I'd utilized it before. The two way on-on switch just allowing the preamp to function somewhat as is stock. Hope I make sense. I think you for your skilled advice.
Wayne Parham Messages: 18554 Registered: January 2001
Illuminati (33rd Degree)
I think it will work too. I sometimes parallel the preamp output of a device to two inputs without any sort of buffer amp. That then parallels the input shunts of the two input devices, which are usually around 50kΩ. They aren't always 50kΩ - some are higher, some lower - but the pseudo-standard for unbalanced RCA inputs is 50kΩ.
So when I parallel two inputs, the load drops to 25kΩ. Some devices have a slight but noticeable drop in sound level when I do that. But they don't change their spectral balance, at least not in my experience, not with the gear I've been using. If a device did, then I would know it could not drive the 25kΩ load, and would need to use a buffer amp of some sort.
I think that's the biggest issue. If you can parallel the inputs and the sound doesn't change - you're golden. And since most devices have preamp outputs that could actually drive a much lower impedance than that - most could drive an impedance as low as 1kΩ - having load impedance drop from 50kΩ to 25kΩ is almost insignificant.
Rusty Messages: 984 Registered: May 2018 Location: Kansas City Missouri
Illuminati (2nd Degree)
Thanks both of you for reassuring my little scheme. I was hesitant to just damn the torpedo's and start drilling into the casework without some seasoned reason behind it. I can follow kit plans, but, design wise I'm a tenderfoot. Green light now.
Posting Rules
Members
Search
Help
Register
Login
Get a T-Shirt!
